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On January 11, 2012, at 1000 eastern standard time, a Cessna 150G, N4041J, operated by TENLE Aviation, was substantially damaged during an impact with terrain following a loss of engine power during initial climb near Fitchburg Municipal Airport (FIT), Fitchburg, Massachusetts. The certificated flight instructor received minor injuries and the student pilot was seriously injured. Visual meteorological conditions prevailed, and no flight plan was filed for the instructional flight conducted under Title 14 Code of Federal Regulations (CFR) Part 91.
According to the flight instructor, he and the student met up that morning at Minute Man Air Field (6B6), Stow, Massachusetts, for the instructional flight in the accident airplane. During preflight, the student pilot noticed that the power cord for the engine preheat was in the oil service door but was not plugged in. The outside air temperature at the time was -01 degree Celsius and the engine was cold. He then plugged in the preheater and continued preparing the airplane for the flight lesson. There was frost on the windows, which the student pilot cleaned off. The wings and horizontal stabilizer did not however have any frost on them, as they had been covered.
About 30 minutes later they disconnected the preheater, then got into the airplane and attempted to start it, but it did not start and it took them 4 or 5 attempts with increasing operation of the primer before the engine started. They next taxied to runway 3, and did the pretakeoff checks. During the runup both the magneto check and carburetor heat check were normal and both checks resulted in an rpm drop that was within limits. They then departed for FIT.
After arriving at FIT the student pilot did a touch and go landing, and then entered the traffic pattern to perform another one. Then while on the downwind leg the engine began to run rough so he had the student apply carburetor heat. Then during the climb after the second touch and go landing, the engine began to run rough. The flight instructor took control of the airplane, lowered the angle of attack, and applied carburetor heat by pulling out the carburetor heat knob. The engine "immediately ran rougher" and the flight instructor pushed in the carburetor heat knob. The engine then ran "less rough" but still ran rough.
The flight instructor then looked over the nose and observed that he had a minimal amount of runway left and that a tractor was also off the end of the runway. He decided that there was not enough runway to land. He was not sure how much power the engine was producing or if he could maintain level flight. He thought about turning back but decided against it. He felt that he was "low and slow' and decided to continue straight ahead. He tried to keep the airplane flying and was successful for about 15 to 20 seconds but then he observed a warehouse ahead of them and banked to the right to avoid it. The airplane then settled and struck trees.
According to the student pilot, he arrived early for his lesson to conduct preflight activities. He indicated that it was a cold morning and had looked at the Aviation Digital Data Service (ADDS) for weather information. He removed and stowed the wing covers and conducted a walk around inspection. When checking the oil level he noted that the engine pre-heat cord had come unplugged overnight. He reconnected the power cord and completed his preflight. No other issues were noted by him.
He indicated that cold weather starting procedures were utilized, which included priming and pulling the propeller through by hand. It took several attempts to start the engine. The engine was warmed up for several minutes prior to conducting the magneto checks. It was noted that the engine revolutions per minute (RPM) dropped 75 to 100 RPM when each magneto was checked, and when carburetor heat was applied, a 100 RPM drop was noted.
They departed 6B6 at approximately 0900 and headed West toward FIT. They approached FIT on a 45 degree downwind for Runway 32 for their first planned Touch and Go. As they turned onto the downwind leg, he noted that the engine briefly exhibited a hesitation. He applied the Carburetor Heat at that point, and kept it on until touchdown.
After conducting a second Touch and Go he noted that after takeoff, the RPM was slowly dropping and the engine was rough. He stated that their altitude at the time was 100 feet above mean sea level (msl). The flight instructor then took the controls from him and applied carburetor heat, which made the engine roughness worse. The flight instructor "immediately" placed the Carburetor Heat to “Off” and pumped the throttle several times in an attempt to get the engine to smooth out. The student pilot then began looking for a place that they could attempt a landing and pointed out the dirt parking lot directly ahead of them, and then they banked to avoid a warehouse, and landed on some trees before settling to the ground.
According to a witness, the airplane was observed at low altitude not much higher than the surrounding buildings. The engine was sputtering and also was much quieter than other airplanes that he had observed. Just prior to impact, the aircraft smoothly banked to the right and disappeared from his view. According to another witness who also observed the airplane, he heard the engine "sputtering", and "popping", and from his vantage point, he observed that it was in a nose high attitude, swaying from side to side, and "coming down fast" just prior to him hearing the sound of the airplane impacting the trees.
According to Federal Aviation Administration (FAA) and pilot records, the flight instructor held a commercial pilot certificate with ratings for airplane single-engine land, airplane multi-engine land and instrument airplane. He also held a flight instructor certificate with ratings for airplane single, airplane multi, and instrument airplane. His most recent FAA second-class medical certificate was issued on November 22, 2011. He reported 1,391 total hours of flight experience with 131 total hours in the accident airplane make and model.
According to FAA and pilot records, the student pilot had accrued approximately 20 total hours of flight experience in the accident airplane. His most recent FAA third-class medical certificate was issued on June 17, 2010.
The accident airplane was a two place, strut braced, high wing airplane of conventional metal construction. It was designed for flight training, air touring, and personal use. It was equipped with tricycle landing gear and powered by an air cooled, 100 horsepower, Continental O-200-A, engine, driving a fixed pitch propeller.
According to the flight instructor, since his purchase of the airplane in August of 2011, he had a number of maintenance issues related to navigation, communication, the vacuum system, and the engine starter. He also advised that he had recent trouble with the carburetor heat sticking, and that the engine had been overhauled shortly before he had purchased the airplane.
The student pilot stated that had not noted any major maintenance issues. He had added oil as needed during preflights. He indicated that early in his flight training, he was noting water in fuel sump samples that he took as part of his preflight activities. The flight instructor subsequently had the overwing fuel cap seals replaced which rectified the problem. He also stated that a radio had been missing from the panel for awhile, the attitude indicator at times was unresponsive, the vacuum system indicated low at times, and the left and right fuel tank quantity gauges did not indicate the fuel quantity that was visually observed in the fuel tanks.
According to FAA and maintenance records, the airplane was manufactured in 1966. The airplane’s most recent annual inspection was completed on August 11, 2011. At the time of the inspection; the engine had accrued 105 hours of operation since major overhaul and the airplane had accrued 4,725.3 total hours of operation.
On November 4, 2011, the carburetor airbox, valve shaft, and bearings, were replaced along with installation of a new carburetor heat cable.
The recorded weather at FIT, at 0952, about 8 minutes prior to the accident, included: calm winds, 10 miles visibility, overcast clouds at 10,000 feet, temperature 0 degrees C, dew point - 04 degrees C, and an altimeter setting of 30.12 inches of mercury. The relative humidity was 72%.
Fitchburg Municipal Airport was uncontrolled and had two runways configured in a 2/20 and 14/32 configuration. Runway 32 was asphalt, in good condition. It was marked with non-precision runway markings and total length was 4510 feet long and 100 feet wide. Obstructions existed off the departure end of 32 in the form of 50 foot high trees, 600 feet from the runway, 125 feet right of centerline, which took an 8:1 slope to clear.
The airplane was not equipped with a flight recorder nor was it required to be under the CFRs. The student however had a Contour Nflightcam onboard which was capable of recording video and contained a built-in global positioning system (GPS) which was capable of recording speed, elevation, and distance.
Examination of data captured from the accident flight revealed that no video or audio was recorded. However, the video did come on after the airplane struck trees and came to rest.
According to the captured GPS data, the airplane touched down in the first 1/3rd of the runway at approximately 09:57:51. Then after passing midfield, the airplane became airborne once again and accelerated until reaching a peak recorded GPS altitude of 500 feet and a peak recorded groundspeed of approximately 56 knots. Shortly thereafter, the airplane began to decelerate and descend, and at 09:59:51 had decelerated to a ground speed of approximately 40 knots. Impact with the trees and ground occurred at approximately 10:00:03, and the airplane came to rest approximately 2,379 feet off the departure end of Runway 32.
WRECKAGE AND IMPACT INFORMATION
Examination of the accident site revealed that the aircraft came to rest in an upright position in a dirt parking lot, partially entangled in a hedgerow and trees. Further examination revealed that the airplane had impacted a number of approximately 20 foot high trees during the accident sequence, starting approximately 50 feet to the south of the accident site. No evidence of propeller strikes on the trees was discovered.
Examination of the wreckage revealed no evidence of any preimpact failures or malfunctions of the airplane. The left and right wings had remained attached to their mounts but the empennage had been torn from the fuselage at a 45 degree angle to aircraft right, just aft of the passenger cabin rear bulkhead. All control cables and electrical harnesses contained in the empennage were intact, and the control cables all had continuity to their respective control surfaces.
The left and right main landing gear assemblies were intact and the tires were in contact with the ground. The nose strut was folded under to the rear and was trapped under the cowling and fuselage. The engine mount tubing exhibited bending and breaking adjacent to the nose strut mounting point.
The nose wheel assembly was located several feet aft of the right wingtip. The nose wheel axle, yoke and wheel collars were also located in the same general area. All tires were noted to be intact and holding pressure.
Examination of the left wing revealed extensive structural damage to the outboard 4 to 5 feet of the wing consistent with striking the trees and hedgerow. The left trailing edge flap was positioned at approximately 5 degrees down. It exhibited heavy damage along the inboard 2 Ft of the trailing edge. Accordion buckling was noted at the same location. Fuel was noted to be intermittently dripping from the left wing fuel tank vent. When the aircraft was lifted to horizontal and placed on cribbing, the dripping stopped. A sample was taken from the fuel tank sump point. It was noted to be clear blue fluid consistent with 100LL aviation fuel. No sediment, water or other contaminants were noted.
Examination of the right wing revealed that it had sustained impact damage to the leading edge starting at the lift strut and terminating near the wingtip. The wingtip exhibited a slight downward bend when viewed from the outboard end. The right aileron was free to travel on its hinges and did not exhibit continuity to either control yoke. There were multiple dents and wrinkles along the full length its trailing edge. The right wing flap was noted to be intact and was in the full up position. A sample was taken from the fuel tank sump point. It was noted to be clear blue fluid consistent with 100LL aviation fuel. No sediment, water or other contaminants were noted.
Examination of the empennage indicated that the rudder was in the full right position and had only superficial damage to the lower edge and plastic upper fairing. The left horizontal stabilizer exhibited crush damage along the entire length of its leading edge. The right horizontal stabilizer as well as the left and right elevator had only superficial damage. Both elevators were free to move on their hinges and continuity was established to the break in the empennage at the aft cabin bulkhead.
Examination of the cockpit revealed that the fuel selector was in the “OFF” detent position. The Fitchburg Fire Department Battalion Chief stated that the CFI had placed the selector to off at his request. Both cabin doors were found to be jammed in the full open position. Both sets of seat belts were noted to be intact. The left half of the forward windscreen was broken out and was discovered 10 Ft forward of the wreckage. It was noted that there was an opening in the instrument panel below the VHF/COMM which appears to be an opening mounting point for a second radio. A digital Contour NFlightCam, equipped with GPS, was located on the ground adjacent to the broken section of windscreen.
Cockpit controls were noted to be in the following positions:
• Ignition – OFF, Key missing
• Master Switch – OFF
• Throttle – 7/8 open
• Mixture – Full Rich
• Carburetor Heat – OFF
• Navigation Lights – ON
• Rotating Beacon – ON
• Wing Flaps – Toggle switch found in Neutral position.
• Elevator Trim – on the Takeoff Bug (Neutral).
When actuated through their full range of motion, the left and right control yokes showed continuity with the elevator. Continuity with the ailerons could not be physically established however, visual examination of the aileron cables revealed that they had failed in tensile overload, and continuity could be established visually from the ailerons to the breaks in the cables, and from the breaks to the control wheels. Both sets of rudder pedals were found in the neutral position. Continuity with the rudder was confirmed.
Propeller and Engine Examination
Examination of the propeller and engine did not reveal any evidence of any preimpact mechanical malfunctions or anomalies.
The propeller spinner and backing plate were intact. The cowling was found with superficial damage on the lower half, consistent with impact. One propeller blade had gouges and scratches on the outboard 10 inches of the leading edge at a 45 degree angle to the edge. The outboard 12 inches of the blade were smoothly folded forward without twisting. A slight leading edge twist was noted at the very tip. Chordwise scratching and mud splatter consistent with dragging on the ground were present at the bend. The other propeller blade was found folded forward at a 90 degree angle with “S” bending along the outboard 26 inches of the blade. Impact damage was noted at multiple places along this section of the blade, and chordwise mud splatter was evident on the rear of the blade. A small section on the tip leading edge was torn away.
The oil level was found at the 6 Quart mark on the dipstick. The oil was clean and no visible signs of contamination were noted. All external engine components were intact, and the starter was noted to be new. The rocker box covers and pushrod tubes were undamaged. The engine exhibited compression on all four cylinders and movement was observed on all rocker arms and valves and drive train continuity to the accessory section was established.
The engine was rotated by hand via the propeller and continuity to the accessory section was established. Thumb compression was obtained on all four cylinders and movement was observed on all rocker arms and valves. The cylinders were inspected using a lighted bore scope and exhibited normal operating signatures and light colored combustion deposits.
The carburetor air box exhibited impact damage and was crushed upward and aft. The foam air filter was present on the face of the airbox. The intake manifold exhibited impact damage in the area of the carburetor mounts and the exhaust system exhibited impact damage and crushing.
The carburetor remained attached to the intake manifold assembly. There was a minor amount of fuel in the carburetor fuel bowl that tested negative for water contamination using water finding paste. The needle valve and seat exhibited normal operating signatures. The floats were immersed in water and showed no signs of leakage. The mixture control arm of the carburetor was found against the right side stop. The mixture control cable was found severed at the control arm attach point and exhibited a fresh break, and the carburetor heat control cable, was found to be intact with its control arm bent toward the right side of the airplane at a 45 degree angle. Despite the damage, it was discovered that, the throttle control arm, mixture control arm, accelerator pump, and carburetor heat control, could all still be moved by hand.
The right magneto remained attached to the accessory case. Impulse coupling engagement was observed and the magneto produced spark on upper spark plug leads when the engine was rotated with the propeller. The left magneto also remained attached to the accessory case. Impulse coupling engagement was observed and the magneto produced spark on upper spark plug leads when the drive train was rotated with the propeller.
The top spark plugs were removed and exhibited light colored combustion deposits. The spark plug electrodes were worn out – normal when compared with a Champion AV-27 Check A Plug Chart. The bottom spark plugs were inspected using a lighted borescope. They exhibited light colored combustion deposits and worn out – normal electrodes. The ignition harness exhibited normal operating signatures.
SURVIVAL FACTORS INFORMATION
The Emergency Locator Transmitter (ELT) did not activate and was noted to be in the “Armed” position. There was no visible damage to the ELT which was found secured in its mounting bracket in the aft passenger cabin.
Upon impact with the ground, both cabin doors opened and the flight instructor and student were able to egress through their respective doors.
During the impact sequence, the student pilot received a cut on his head, pelvic injuries, and a broken knee.
Examination of the restraint system revealed that the lap belts had been manufactured in 1972 and that no shoulder harnesses were installed.
According to the FAA Civil Aerospace Medical Institute's publication AM-400-90/2, seat belts will only protect occupants in minor impacts; however the use of shoulder belts will reduce major injuries by 88 percent and fatalities by 20 percent.
TESTS AND RESEARCH
The Cessna Integrated Flight Training System, Manual of Flight (CE315344G), states in part that, the cooling effect of fuel vaporization and the air pressure drop across the venturi in the carburetor throat can chill intake air considerably. If the air is moist, moisture may condense and accumulate in the carburetor and intake duct as frost or ice. Even a slight amount of ice will reduce power, and a continued accumulation may lead to engine failure.
Carburetor ice can occur without visible moisture and even when temperatures are more than 90 degrees F. The danger of carburetor ice is greatest in humid air, at outside air temperatures below 60 degrees F.
Carburetor ice is also more likely to occur at low power settings, and icing symptoms may not be detectable on extended descents.
Carburetor Heat System
To eliminate carburetor ice, a carburetor heat system was installed in the airplane. Outside air was ducted to a heater muff where the air was heated to a temperature that would melt ice. After the air was heated it was routed to a valve that was controlled by a carburetor heat control located on the instrument panel.
Pulling out the carburetor heat control would open the carburetor heat valve and let hot air pass through the carburetor where it would melt the ice, mix with the fuel, and continue on to the engine cylinders. Some loss of power would be noticed when using carburetor heat as less oxygen would be available to the fuel-air mixture since hot air is less dense than cold air.
If the airplane is not equipped with a carburetor air temperature gauge, partial application of carburetor heat should be avoided. This is because partial heat may raise the temperature of the incoming air sufficiently to permit carburetor icing.
Application of carburetor heat causes an immediate small reduction in power. If ice is not present in the carburetor, the power reduction remains constant. When ice is present, application of carburetor heat may cause the engine to run rough as the ice melts and is carried into the engine. In this case the engine will run rough until the ice has been melted.
Continental Motors Guidance
According to the Continental Motors Operator's Manual for the O-200-A (P publication X30012), carburetor ice can form on the ground with the engine idling. Therefore just before takeoff and during the magneto check, the carburetor heat control should be positioned to "ON", and it should be left in that position until the throttle is advanced for the takeoff run, then the carburetor heat control should be positioned to the "cold air" (off) position. This gives maximum power for takeoff. The engine should be monitored for any indication of ice (roughness or loss of RPM) during climb and full carburetor heat should be applied at the first sign of icing. The correct way to use carburetor heat is to first apply full heat to remove any ice that has formed. Determine the minimum amount of heat required to prevent ice forming, each time removing any ice that has formed by applying full heat.
Furthermore, the guidance goes on to say that, during descent and landing if a long glide is made to apply power at short intervals to clear the cylinders and retain engine temperatures in the event that instant power is required and that carburetor heat is available only at engine outputs well above idle. Carburetor heat should be applied before closing the throttle and should be "OFF" before opening the throttle so full power will be available if necessary.
FAA Advisory Circular 91-51A (Effect of Icing on Aircraft Control and Airplane Deice and Anti-Ice Systems), also states in part that; there are two kinds of icing that are significant to aviation: structural icing and induction icing. Small aircraft engines commonly employ a carburetor fuel system or a pressure fuel injection system to supply fuel for combustion. Both types of induction systems hold the potential for icing which can cause engine failure. The pilot should be aware that carburetor icing can occur at temperatures between -7°C (20°F) and +21 °C (70°F) when there is visible moisture or high humidity. This can occur in the carburetor because vaporization of fuel, combined with the expansion of air as it flows through the carburetor, causes sudden cooling, sometimes by a significant amount within a fraction of a second. Carburetor ice can be detected by a drop in rpm in fixed pitch propeller airplanes and a drop in manifold pressure in constant speed propeller airplanes. In both types, usually there will be a roughness in engine operation.
According to FAA's Winter Flying Tips (FAA P-8740-24), partial throttle (cruise or letdown) is the most critical time for carburetor ice. The recommended practice is to apply carburetor heat before reducing power and to use partial power during letdown to prevent icing and overcooling the engine.
The FAA also advises that to prevent carburetor ice to use carburetor heat ground check, to use heat in the icing range, and to use heat on approach and descent.
To be aware of the warning signs of carburetor ice including, loss of rpm (with a fixed pitch propeller) or a drop in manifold pressure (with a constant speed propeller); rough running.
The pilot response to these warning signs should be to apply full carburetor heat immediately (the engine may run rough initially for a short time while the ice melts).
Carburetor Icing Probability Chart
A check of a carburetor icing probability chart revealed that at the time of the accident the ambient temperature and dew point favored serious icing.
During the on-scene portion of the examination no indications of fresh or existing oil/fluid leaks were noted to be present on the engine or within the cowling. However after the wreckage was recovered, fuel and oil staining was observed on the lower cowling and belly of the airplane and a fuel line from the fuel separator was found to be disconnected from the carburetor. This was later determined to have occurred when the recovery crew had disconnected the fuel line to drain fuel from the airplane for transport.